The expression is certainly American, turning up at various times in the south and west of the country... In the negative it meant something hadn’t yet been made fully ready — a football coach commented on one of his young players in the Charleston Gazette in 1972 that “He has a long way to go. He hasn’t been saucered and blown yet.”..
The idea goes back a long way, of course, much further than the expression itself. A squib appeared in a British newspaper two centuries ago, in which a Frenchman asked a friend to advise on the correctness of his manners at dinner:
“And the coffee?” “There I am certain I was right; it was boiling hot, and I poured it in small portions into my saucer.” “Which was what no one else did; every body takes his coffee in his cup, and never in his saucer.” The Courier (Middlesex), 21 Mar. 1826.
The link concludes with an (?)apocryphal story about George Washington saying "“we pour our legislation into the Senatorial saucer to cool it.”